1. Field of the Invention
This invention relates to an interconnection structure. More particularly, the invention relates to an interconnection structure comprising a metal film which is formed by etching an etched member formed from a metal, which can form a high vapor pressure halide, with a halogen-containing source gas plasma under predetermined conditions.
The present invention further relates to the method and the apparatus useful when applied in producing a film of a composite metal by etching an etched member having a plurality of metals with a source gas plasma containing a halogen, in particular.
2. Description of the Related Art
In producing a metal film, for example, a thin film of copper, by vapor phase deposition, it has been common practice to use an organometallic complex of a liquid, for example, copper-hexafluoroacetylacetonato-trimethylvinyl-silane, as a starting material, dissolve the solid starting material in a solvent, and vaporize the solution by use of a thermal reaction to form a film on a substrate.
High speed semiconductor devices have increasingly used copper, instead of a conventional aluminum alloy, as a material for their interconnection in order to increase the speed of switching, decrease transmission losses, and achieve a high density. In this case, a predetermined interconnection structure is formed by performing vapor phase deposition or plating on an insulating substrate (e.g., SiO2) having depressions for interconnection, such as trenches or holes (via holes), on its surface, thereby adhering copper onto the surface of the substrate, including the depressions.
In producing a thin film of copper by vapor phase deposition, it has been common practice to use an organometallic complex of a liquid, for example, copper-hexafluoroacetylacetonato-trimethylvinylsilane, as a starting material, dissolve the solid starting material in a solvent, and vaporize the solution by use of a thermal reaction to form a film on the substrate.
The damascene method is frequently used in forming a predetermined copper interconnection structure by burying copper in the depressions of the substrate. The damascene method is a technique which cuts trenches in an insulating film, buries copper, an interconnection material, in the so formed trenches by use of vapor phase deposition or plating, and removes a surplus thin copper film outside the trenches by CMP (chemical and mechanical polishing) to obtain a predetermined interconnection structure.
With the above-mentioned earlier film formation technologies, it has been difficult to increase the speed of film formation, because the film is formed with the use of a thermal reaction. Moreover, the metal complex as the starting material is expensive. In addition, hexafluoroacetylacetonato and trimethylvinylsilane accompanying copper remain as impurities in the thin film of copper, presenting difficulty in improving the quality of the film.
On the other hand, the above-described interconnection structure obtained by the earlier technologies is formed by adhesion of a thin copper film on the surface of the substrate, thus posing the problem that the burial characteristics of copper are poor. In recent years, the width of the interconnection has tended to become smaller. In response, the holes need to be decreased in diameter. As a result, the aspect ratio, the ratio of the depth to the diameter of the hole, must be minimized. For this purpose as well, it is an urgent task to improve the burial characteristics.
Moreover, the interconnection structure obtained by the earlier technologies comprises relatively small copper crystal grains, so that many grain boundaries exist among the grains. Thus, electromigration is liable to cause a local high-resistance portion in the grain boundary or the defective site, and in the worst case, poses the problem that this portion is broken by Joule's heat. At the same time, stress migration due to residual stress produced during burial of the copper film in the depression may lead to physical breakage.
With the above-mentioned vapor phase deposition method, moreover, it has been difficult to increase the speed of film formation, because the film is formed with the use of a thermal reaction. Besides, the metal complex as the starting material is expensive. In addition, hexafluoroacetylacetonato and trimethylvinylsilane accompanying copper remain as impurities in the thin film of copper, making it difficult to improve the quality of the film.
In forming the interconnection by the damascene method, there is also the problem that the CMP step is absolutely necessary, requiring a long time for the formation of the interconnection structure. This is a major drawback with a multilayer interconnection structure which has tended to be increasingly used in recent years. The reason is that a single-layer interconnection structure can be formed by the single damascene method, while a two-layer interconnection structure can only be formed by the double damascene method requiring the same procedure to be performed twice, meaning that as the number of the layers increases, the number of the CMP steps performed increases proportionally.